Members of South Africa's striking mining union AMCU have rejected the latest wage offer from the world's top-three platinum producers, its president said, extending a crippling 14-week stoppage.

"The members have rejected the offer from the employer," Joseph Mathunjwa told reporters after addressing a rally of workers near Lonmin's Marikana mine. The Association of Mineworkers and Construction Union (AMCU) held similar rallies in recent days at Anglo American Platinum and Impala Platinum.

It now plans to meet with the companies to inform them in person of the rejection, Mathunjwa said.

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Wage talks collapsed last week, dashing hopes for an imminent end to South Africa's longest and most costly mining strike, which has hit 40 per cent of global platinum production.

The companies say they are taking their offer directly to the workers via cellphone text messages and radio and newspaper spots in a bid to circumvent AMCU's leadership, setting the stage for a showdown between capital and labour.